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 Question from cherrielyn, a student: Assuming that earth is a sphere of radius 6380 km, what is the difference in the latitudes of two cities 270 miles apart positioned on the same meridian? Thank you in advanced po! :)

First, the picture. "Meridian" comes from the word for "noon" - it's a line of places that all have solar noon at once, that is, a north-south line, a line of constant longitude. As a result, they are all the same length - unlike "parallels", lines of constant latitide, which get smaller as you approach the poles. And that common length is the length of a great circle.

it would help to have the same units. So how many km is 270 miles?

If the Earth has radius 6380 km, what is its circumference? [You should get a surprisingly round number. Look up the history of the meter to see why.

There are 360 degrees in a circle: how many kilometers to a longitudinal degree?

Good hunting!
RD

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